First of all, you will need to verify yourself (mobile phone SMS, drivers license / ID, etc) and then you will be able to get a bitcoin credit card. You will need to pay a fee depending on the credit limit - if you want a credit limit of 10 BTC (for example) you would need to pay 5 BTC up front in fees.
Why would you do that? Well, let's say you get paid in the 1st and 14th, and it takes a few days for you to get bitcoins on mtgox after a bank transfer. You want to buy something on the 8th. Pay it back in 30 days and no interest
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
Would anyone be interested? It's not going to be an actual physical credit card, just a wallet where you can spend more than what you actually have.